1. Field of the Invention
The present invention relates to a method of reducing the temperature difference between a pair of substrates, and more particularly to a method of mitigating heat transfer inhibition caused by particles caught between the pair of substrates in which heat is transferred through the contact surface between the substrates, and a fluid reaction device using the same.
2. Description of the Related Art
For example, a biochemical reaction such as a polymerase chain reaction (“PCR”) requires a microfluidic reaction chip that accommodates a small amount of biochemical fluid, and a heater that periodically heats the microfluidic reaction chip while the heater contacts the microfluidic reaction chip. A lower portion of the microfluidic reaction chip that contacts the heater, and an upper portion of the heater that contacts the lower portion of the microfluidic reaction chip can be formed of a flat substrate. The substrate material can be silicon (Si) of a high thermal conductivity. In order to perform the biochemical reaction, the microfluidic reaction chip should be positioned to make a close contact with a substrate disposed on the upper portion of the heater and then heat generated from the heater is transferred to the microfluidic reaction chip.
FIG. 1 is a diagram illustrating a temperature difference between a pair of substrates 1 and 2, which is caused by particles 5 caught between the pair of substrates 1 and 2.
Referring to FIG. 1, in the case of a substrate 1 disposed on the upper portion of a heater and a substrate 2 disposed on the lower portion of a microfluidic reaction chip as described above, particles 5, such as dust, could be caught between the pair of substrates 1 and 2 such that the particles would prevent heat transfer between the pair of substrates 1 and 2. That is, when the particles 5 are caught between a pair of the substrates 1 and 2, which are made of a hard material such as silicon (Si), an air layer 7 is formed between the pair of substrates 1 and 2 and prevents heat transfer from the high-temperature substrate 1 to the low-temperature substrate 2, respectively.
In particular, a temperature difference between the pair of substrates 1 and 2 can be calculated by multiplying the power output of the heater (not illustrated) by the thermal contact resistance between the pair of substrates 1 and 2. If a contact area of the pair of substrates 1 and 2 is 100 mm2, a thickness G1 of the air layer 7 formed by the particles 5 is 10 microns (μm) and thermal conductivity of air is 0.031 W/(m·K) at 92 Celsius (° C.), the thermal contact resistance between the pair of substrates 1 and 2 can be estimated as 3.2 Celsius/watt (° C./W). Therefore, when the power output of the heater is 1 W, the temperature difference between the pair of substrates 1 and 2 is 3.2° C., and when the power output of the heater is 5 W, the temperature difference between the pair of substrates 1 and 2 is 16.0° C., and so on.
To reduce the thermal contact resistance caused by the caught particles, a method of using thermal grease at the interface, or a method of bonding the two substrates by thermal epoxy is conventionally used. However, when frequent contact and separation between a pair of substrates occurs as in the case of a microfluidic reaction chip and a heater, the thermal grease or thermal epoxy cannot be applied and it is highly possible that particles will be caught between the pair of substrates. Therefore, in order to reduce the effect of caught particles on the temperature difference between the pair of substrates, the contact surfaces where the microfluidic reaction chip makes contact with the heater must be carefully wiped and cleaned before the microfluidic reaction chip is mounted on the heater. However, such a method is not reliable because it is very inconvenient for users, since particles that users fail to wipe off still may exist even though the particles on the substrates have been completely wiped, in addition there also exists a possibility that new particles may be caught during the microfluidic reaction chip mounting on the heater.